A system which can efficiently compress any one of a multivalue image and a binary
image and can preferably keep a high picture quality is provided. To accomplish
this object, the system has means for generating conversion coefficients of M values
by converting input image data by a first system, means for generating conversion
coefficients of N values (NM) by converting the input image data by a second
system and means for outputting first information showing a position where a significant
conversion coefficient exists in a block constructed by the conversion coefficients
of M values or the conversion coefficients of N values and second information showing
the significant conversion coefficient. Block division information which is generated
by a block dividing process as an element technique of the image encoding system
is efficiently entropy encoded. To accomplish it, the system has means for outputting
division information showing whether each of a plurality of blocks including an
encoding subject block has further been divided into a plurality of blocks or not
and means for entropy encoding the division information corresponding to the encoding
subject block on the basis of a presumption probability according to a division
situation of a neighboring block of the encoding subject block.
